Two amino acids in each of D1 and D2 dopamine receptor cytoplasmic regions are involved in D1–D2 heteromer formation

D1 and D2 dopamine receptors exist as heteromers in cells and brain tissue and are dynamically regulated and separated by agonist concentrations at the cell surface. We determined that these receptor pairs interact primarily through discrete amino acids in the cytoplasmic regions of each receptor, with no evidence of any D1–D2 receptor transmembrane interaction found. Specifically involved in heteromer formation we identified, in intracellular loop 3 of the D2 receptor, two adjacent arginine residues. Substitution of one of the arginine pair prevented heteromer formation. Also involved in heteromer formation we identified, in the carboxyl tail of the D1 receptor, two adjacent glutamic acid residues. Substitution of one of the glutamic acid pair prevented heteromer formation. These amino acid pairs in D1 and D2 receptors are oppositely charged, and presumably interact directly by electrostatic interactions.

► Pair of adjacent arginines of the D2 receptor involved in forming heteromers with the D1 receptor.
► D2 receptor with one arginine substituted did not form heteromers with the D1 receptor.
► Pair of adjacent glutamic acids in the D1 carboxyl tail involved in forming D1–D2 heteromers.
► D1 receptor with one of the glutamic acids substituted did not form D1–D2 heteromers.
► Aspartic acid substituted for glutamic acid in the D1 carboxyl tail did not form heteromers.